19 days past ovulation and 4 BFNs. What’s going on!?

Monique

I have NEVER had irregular periods. My cycle is usually 28 days, sometimes 29-30. I am now 19 DPO. AF was supposed to start Thursday 2/14. I’m now 5 days late. I have taken multiple tests. 2 tests on Saturday, 1 on Sunday, and one yesterday (Monday), and all have been a BFN! I’m puzzled. Anybody else with very regular periods have this happen before? I’m concerned.